Multi-stage wastewater treatment system

ABSTRACT

Methods, systems, and/or apparatuses for treating wastewater produced at a thermoelectric power plant, other industrial plants, and/or other industrial sources are disclosed. The wastewater is directed through a wastewater concentrator including a direct contact adiabatic concentration system. A stream of hot feed gases is directed through the wastewater concentrator. The wastewater concentrator mixes the hot feed gases directly with the wastewater and evaporates water vapor from the wastewater. The wastewater concentrator separates the water vapor from remaining concentrated wastewater. A contained air-water interface liquid evaporator may be arranged to pre-process the wastewater before being treated by the wastewater concentrator.

FIELD OF THE INVENTION

The present invention relates generally to methods, systems, and/orapparatuses for treating wastewater including a plurality of processingstages.

BACKGROUND

Thermoelectric power plants, including hydrocarbon-fired power plants,such as coal, oil, and/or natural gas-fired power plants, and nuclearpower plants, and other heavy industrial processes use very largeamounts of water for performing various processes and for providingancillary function. Often, the water is withdrawn from the surroundingenvironment, such as a nearby stream or lake, and the water iseventually returned to the stream or lake.

A problem is that the water often becomes contaminated with chemicalsand/or other waste products from the industrial process, thereby formingwastewater. It is, therefore, often necessary to process this wastewaterto remove some or all of the contaminants prior to returning thewastewater to the environment.

One particular source of wastewater often generated in ahydrocarbon-fired thermoelectric power plant is flue gas desulfurization(“FGD”) purge water, or “blowdown”. FGD purge water is a wastewater orslurry containing sulfur and/or other chemicals removed from a stream offlue gases, i.e., exhaust gases from a boiler or other hydrocarbon-fuelcombustion process. FGD purge water is a byproduct of a flue gasdesulfurization system, in which sulfur and other contaminants areremoved from a flow of flue gases, usually in a component called anabsorber. In the absorber, sulfur and/or other contaminants are removedfrom the flue gases, usually by spraying a stream of flue gases with awater-based slurry carrying various chemicals designed to help removethe sulfur and/or other contaminants from the gases. The slurry iscollected after being sprayed into the stream of flue gas and typicallyis recycled many times through the absorber. FGD purge water is awastewater stream that is drawn off of the slurry as the buildup ofsulfur and/or other contaminants in the slurry increases, for example,to maintain the total dissolved solids (“TDS”) in the slurry within somepreselected range or under some preselected upper limit.

Another source of wastewater often generated in electrical power plantsand other industrial plants is cooling tower purge water, or “blowdown.”Similar to the FGD purge water, cooling tower purge water is wastewatercontaining dissolved solids that is drawn off of a supply of water usedfor cooling exhaust gases, usually to maintain the TDS in the coolingwater within or under some preselected range or limits.

A further source of wastewater often generated in power plants isservice water, which is used to cool various heat exchangers or coolersin the power house or elsewhere, other than the main condenser. As withthe FGD purge water and the cooling tower purge water, the service waterusually accumulates dissolved solids, the levels of which usually needto be controlled.

The service water, FGD purge water, and cooling tower purge waterusually need to be treated to remove some or all of the dissolved solidsbefore being returned to the environment or recycled for further usewithin the industrial plant.

SUMMARY

According to some aspects, one or more methods, systems, and/orapparatuses are disclosed for treating wastewater at a thermoelectricpower plant with a wastewater concentrator including a direct contactadiabatic concentration system prior to returning the water to thesurrounding environment or recycling the water for further use withinthe power plant. The methods, systems, and apparatuses may be applied toother processes that produce a stream of wastewater containing sulfur orother sour gas, for example, petrochemical refineries and/or natural gasprocessing plants.

According to other aspects, one or more methods, systems, and/orapparatus are disclosed for treating wastewater in a multi-stagetreatment system, wherein a first stage includes a liquid evaporatoroperatively disposed in a reservoir of wastewater, and a second stageincludes a wastewater concentrator operatively connected to thereservoir to receive wastewater from the reservoir. The multi-stagetreatment system can be used as part of the systems for treatingwastewater at a thermoelectric power plant, but is not limited to use inthe thermoelectric power plant.

According to one exemplary aspect, a wastewater treatment system for athermoelectric power plant includes a stream of wastewater generated ina thermoelectric power plant that is directed through a wastewaterconcentrator implementing a direct contact adiabatic wastewaterconcentrator system. A stream of hot feed gases is simultaneouslydirected through the wastewater concentrator. The wastewaterconcentrator mixes the hot feed gases directly with the wastewater andevaporates water from the wastewater to form water vapor andconcentrated wastewater. The wastewater concentrator separates the watervapor from the concentrated wastewater. The wastewater concentratorexhausts discharge gases, including the water vapor and some or all ofthe feed gases. The discharge gases may be exhausted to atmosphere or toanother component for further processing, recovery, or use. Theremaining concentrated wastewater, or discharge brine, may be recycledthrough the wastewater concentrator for further concentrating and/ordirected for further processing, recovery, and/or disposal.

According to another exemplary aspect, a method of processing wastewaterfrom a thermoelectric power plant with a wastewater concentratorimplementing a direct contact adiabatic wastewater concentrator systemis disclosed. The power plant includes a source of wastewater and asource of hot feed gases. The method includes the steps of receiving astream of the hot feed gases into the wastewater concentrator, receivingfeed wastewater including the wastewater through a conduit from thethermoelectric power plant into the wastewater concentrator, mixing thehot feed gases directly with the feed wastewater in the wastewaterconcentrator to evaporate water vapor from the feed wastewater,separating the water vapor from the feed wastewater in the wastewaterconcentrator to form concentrated discharge brine and discharge gases,and exhausting the discharge gases from the wastewater concentrator.

According to a further exemplary aspect, a thermoelectric power plantincludes thermoelectric generator, such as a boiler for generating steamto turn a turbine operatively connected to a generator for producingelectricity and/or a gas turbine, a wastewater concentrator having adirect contact adiabatic wastewater concentrator system, a source ofwastewater operatively connected to the wastewater concentrator tosupply feed wastewater to the wastewater concentrator, and a source ofhot feed gases operatively connected to the wastewater concentrator tosupply the hot feed gases to the wastewater concentrator. The wastewaterconcentrator mixes the hot feed gases directly with the feed wastewater,evaporates water vapor from the feed wastewater, separates the watervapor from the feed wastewater thereby forming discharge brine anddischarge gases, exhausts the discharge gases to atmosphere and/oranother process component, and provides the discharge brine for furtherprocessing and/or disposal separate from the discharge gases.

In further accordance with any one or more of the foregoing exemplaryaspects, a system, apparatus, and/or method for treating power plantwastewater and/or a multi-stage wastewater treatment system furtheroptionally may include any one or more of the following preferred forms.

In some preferred forms, the wastewater includes purge water, servicewater, leachate, and/or holding reservoir water from the power plant.The purge water may include flue gas desulfurization purge water fromthe flue gas desulfurization system and/or purge water from a coolingtower.

In some preferred forms, the thermoelectric power plant includes aboiler having a hydrocarbon fired combustion heater for generating thesteam, a first stream of flue gas from the combustion heater, and a fluegas desulfurization system. The flue gas desulfurization system may beoperatively connected to the first stream of flue gas from thecombustion heater. The flue gas desulfurization system may be arrangedto remove sulfur and/or other contaminants from the flue gas, such aswith an absorber, and to generate flue gas desulfurization purge water.The combustion heater may be hydrocarbon-fired, for example, with coal,oil, and/or natural gas. The wastewater concentrator may be operativelyconnected to the flue gas desulfurization system to receive feedwastewater including the flue gas desulfurization purge water. In someforms, the thermoelectric power plant includes other types ofthermoelectric generators, such as a gas turbine. The gas turbine may beused, for example, alone as a primary electric generation plant and/oras a peak shaving or backup electric generation plant in combinationwith other types of thermoelectric generators.

In some forms, the thermoelectric power plant includes a cooling tower.The cooling tower generates the cooling tower purge water. Thewastewater concentrator may be operatively connected to the coolingtower to receive feed wastewater including the cooling tower purgewater.

In some forms, the thermoelectric power plant generates service water.The wastewater concentrator may be operatively connected to a source ofthe service water to receive feed wastewater including the service waterfor concentration.

In some forms, the wastewater concentrator may be operatively connectedwith a source of power plant leachate such that the power plant leachateis supplied to the wastewater concentrator for concentration.

In some preferred forms, the wastewater concentrator may be operativelyconnected with a holding reservoir such that water from the holdingreservoir is supplied to the wastewater concentrator for concentration.

In some preferred forms, the hot feed gases include hot exhaust gases orother waste heat from one or more other processes within the powerplant. The hot feed gases may be drawn from the first stream of fluegas, such as with a slip stream, from heated air from a combustion airpre-heater for the combustion heater, and/or include other hot gasstreams. The hot feed gases may be pulled from the first stream at atemperature of between approximately 150° F. and approximately 800° F.The slip stream may draw from the first stream after the first streamhas passed through a combustion air pre-heater for pre-heatingcombustion air for a burner. The slip stream may draw from the firststream before the first stream reaches the flue gas desulfurizationsystem. The combustion heater may include any one or more of acoal-fired boiler, an internal combustion engine, a turbine stack, andother combustion devices. The boiler may include a boiler for producingfeed steam for a turbine for an electric generator.

In some preferred forms, the hot feed gases are drawn from heated airproduced by the combustion air pre-heater. The heated air from thecombustion air pre-heater optionally may be further heated before beingprovided as hot feed gases, for example, with a flare or a burner.

In some preferred forms, the hot feed gases are direct fired by a flareor burner. The flare or burner may be dedicated for heating the hot feedgases to be provided to the wastewater concentrator.

In some preferred forms, the hot feed gases are drawn from standbygeneration equipment, such as a standby gas turbine, or other peakshaving generation devices.

In some preferred forms, the hot feed gases are drawn from a pluralityof different sources of heated air, including any one or more of thesources described herein.

In some preferred forms, the wastewater concentrator includes a devicethat mixes and evaporates the wastewater directly into the hot exhaustgases, such as a venturi evaporation device or draft tube evaporation.The wastewater concentrator may include any one or any combination ofcross-flow gas-liquid separators, cyclonic gas-liquid separators, or wetelectrostatic precipitators. The wastewater concentrator may bepermanently installed in the electrical power plant. The wastewaterconcentrator may be portable and temporarily installed in the electricalpower plant.

In some preferred forms that form a multi-stage wastewater treatmentsystem the wastewater may be pre-processed at a first stage byadditional wastewater processing systems prior to being provided forprocessing as feed wastewater in the wastewater concentrator at a secondstage. The pre-processing may include a liquid evaporator operativelydisposed in a reservoir of wastewater to evaporate at least some waterfrom the wastewater prior to providing the wastewater to the wastewaterconcentrator. The reservoir may receive wastewater from the power plant,such as by one or more supply conduits. The reservoir may be operativelyconnected to the wastewater concentrator by one or more additionaldischarge conduits. The wastewater may flow into the reservoir from oneor more processes in the power plant via the supply conduits. Thewastewater may flow from the reservoir to the wastewater concentratorvia the discharge conduits. The liquid evaporator is preferablyconnected to a source of forced air and vigorously mixes a discontinuousgas phase with a continuous phase of wastewater inside a partiallyenclosed vessel, such as by forming bubbles of air in a mass of thewastewater. The forced air may be heated, for example, by waste heatsources within the power plant, such flue gas or other waste heatsources. The liquid evaporator may pre-process the wastewater to providea more concentrated feed wastewater to the wastewater concentrator thanby simply the wastewater directly from the various processes in thepower plant as feed wastewater. The combination of a liquid evaporatorused at a first stage to pre-process feed wastewater for the wastewaterconcentrator at a second stage may be implemented in other useenvironments in addition to the thermoelectric power plant of theexamples.

In some preferred forms, the concentrated discharge brine produced bythe wastewater concentrator is post-processed by additional processingsystems and/or methods. The discharge brine may be de-watered in apost-treatment process. Liquid removed from the discharge brine in thepost-treatment process may be recycled to the wastewater concentrator tobe processed again.

In some preferred forms, an electrostatic precipitator (ESP), wetelectrostatic precipitator (WESP), and/or a bag filter is operativelyconnected to the first stream of flue gas or the slip stream of fluegas. The ESP, WESP, or bag filter may be arranged to remove fly ashand/or other contaminates from the flue gas before the flue gas entersthe wastewater concentrator.

In some preferred forms, the discharge gases exhausted from thewastewater concentrator are conducted to one or more additionalemissions control systems for further processing prior to release toatmosphere. The discharge gases from the wastewater concentrator may beheated or re-heated before returning to the plant's exhaust stream. Thedischarge gases may be heated or re-heated with any, or any combinationof burners, electric heaters, or other streams of heated gases. Thedischarge gases may be heated above an acid-gas condensationtemperature. The discharge gases may be returned to the flue gasdesulfurization system. The discharge gases may also or alternatively beexhausted directly to atmosphere without further processing orrecapture.

Other aspects and forms will become apparent upon consideration of thefollowing detailed description and in view of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary hydrocarbon-firedthermoelectric power plant including a system for treating wastewatergenerated by the plant according to some aspects of the presentdisclosure;

FIG. 2 is a schematic diagram of an exemplary system for treating plantwastewater usable in the power plant of FIG. 1;

FIG. 3 is a schematic diagram of the exemplary system of FIG. 2 withadditional optional features shown;

FIG. 4 is an isometric partial cut-away view of an exemplary wastewaterconcentrator adaptable for use in any one of the systems of FIGS. 1-3;

FIG. 5 is a cross-sectional view of pre-processing equipment inaccordance with teachings of the present disclosure including a liquidevaporator operatively disposed in a reservoir;

FIG. 6 is a cross-sectional view of pre-processing equipment inaccordance with teachings of the present disclosure including anotherliquid evaporator operatively disposed in a reservoir; and

FIG. 7 is a side elevation view of another liquid evaporator usable in areservoir as pre-processing equipment.

DETAILED DESCRIPTION

Turning now to the drawings, FIG. 1 shows an exemplary wastewatertreatment system 10 for treating power plant wastewater at athermoelectric power plant 12. The system 10 includes a wastewaterconcentrator 14. The wastewater concentrator 14 is operativelyconnected, such as through a conduit 16, to a stream of wastewaterproduced by one or more processes within the thermoelectric power plant12 at a first inlet 17. The wastewater concentrator 14 is alsooperatively connected, such as through a conduit 18, to a stream of hotfeed gases at a second inlet 19. The wastewater concentrator 14 includesa direct contact adiabatic concentration system, wherein the wastewaterconcentrator 14 mixes a stream of the hot feed gases from the conduit 18directly with a stream of the wastewater from the conduit 16 andevaporates water from the wastewater to form water vapor andconcentrated wastewater. The wastewater concentrator 14 separates thewater vapor from remaining concentrated wastewater from the feedwastewater. The wastewater concentrator 14 exhausts discharge gases,including the water vapor and some or all of the now-cooled feed gases,in a stream of exhaust vapor, such as through a conduit 20, from anexhaust outlet 22. The discharge gases may be exhausted to atmosphere,to the plant exhaust system, such as through a gas flue exhaust stack40, or to another component (not shown) for further processing,recovery, or use. The wastewater concentrator 14 discharges a dischargebrine of the concentrated wastewater through a brine discharge outlet 24that is preferably operatively connected with a conduit 25 arranged totransport the discharge brine away from the wastewater concentrator 14.The conduit 25 optionally operatively connects the discharge brineoutlet 24 to a post-processing system 26 for further processing of thedischarge brine and/or disposal. In some arrangements, the brinedischarge outlet 24 is also or alternatively operatively connected tothe first inlet 17 or a third inlet (not shown) to re-cycle thedischarge brine through the wastewater concentrator 14 for furtherprocessing and concentration.

In a preferred arrangement, the system 10 results in zero liquiddischarge from the thermoelectric power plant 12. In this arrangement,discharge brine from the wastewater concentrator 14 may be recycledthrough the wastewater concentrator 14 until the discharge brine reachesa saturation level of TDS or even a super saturation level of TDS. Thedischarge brine may then be further processed by the post processingsystem 26, with one or more additional dewatering systems, and/or otherwater and/or solids removal systems, for example using acompression-type de-watering system, until all or substantially all ofthe water has been separated from the solids. As the water is separatedfrom solids and continuously returned to the wastewater concentratorthis mode of operation allows zero liquid discharge (ZLD) as theremaining solids can be disposed of in any desirable and appropriatemanner.

The thermoelectric power plant 12 may be any type of power plant, suchas a nuclear power plant or a hydrocarbon-fired power plant. In theexemplary arrangement shown in the drawings, the thermoelectric powerplant 12 is a hydrocarbon-fired power plant. The thermoelectric powerplant 12 includes one or more combustion heaters 30, such as boilers,for heating boiler feed water 31 into steam 33 to turn a generatorturbine (not shown). The boiler 30 discharges a main stream 32 of hotflue gases that passes sequentially through an economizer 34 operativelyconnected to the boiler 30, an air pre-heater 36 for pre-heating boilercombustion feed air, a flue gas desulfurization system (“FGD”) 38 forremoving fly ash and sulfur dioxide from the flue gas, and a flue gasexhaust stack 40 for exhausting the flue gas to atmosphere. The boilers30 may be coal-fired, gas-fired, and/or oil-fired.

In some optional arrangements, the exemplary FGD system 38 includes afly ash removal device 42, such as fabric bag filter, electrostaticprecipitator (“ESP”) or wet electrostatic precipitator (“WESP”),operatively connected to the air pre-heater 36, a wet scrubber 44operatively connected to the fly ash removal device 42, and an absorber46 for removing sulfur oxides operatively connected to the wet scrubber44. As is well understood in the art, a sorbent slurry, such as a slurrycontaining powder limestone, is circulated through the absorber 46 andmixed with the flue gas to draw and precipitate sulfur oxides (SO_(x))and/or other contaminants out of the flue gas. As the slurry isre-circulated through the absorber, the TDS in the slurry increases. Tomaintain the slurry within a preselected range or under a preselectedmaximum TDS concentration, a small amount of the slurry with high TDSconcentration is drawn out of the absorber while fresh makeup sorbentslurry 48 with lower TDS concentration is provided into the absorber 46to maintain the desired TDS concentration of the slurry being circulatedthrough the absorber 46. A product of the SO_(x) precipitate, gypsum 49,can be drawn out from the absorber 46 for subsequent use, sale, ordisposal.

The thermoelectric power plant 12 and the FGD system 38 described hereinare meant only to provide sufficient exemplary background forunderstanding how the wastewater treatment system 10 can be integratedinto the thermoelectric power plant 12 to treat the wastewater producedtherein. It is understood that the thermoelectric power plant 12 and theFGD system 38 may include additional and/or alternative components in amanner well understood in the art and not the further subject of thisapplication.

The high TDS concentration slurry drawn from the absorber 46, calledflue gas desulfurization (FGD) purge water, or “blowdown,” isoperatively conducted via one or more conduits 16 to the inlet 17 to besupplied as feed wastewater to the wastewater concentrator 14. Hot feedgases are also supplied to the inlet 19 by one or more conduits 18 fordirect mixing with the feed wastewater inside the wastewaterconcentrator 14. Preferably, both the hot feed gases and the feedwastewater are supplied to the wastewater concentrator 14 continuouslyand simultaneously to promote continuous direct mixing and evaporation.

In an optional multi-stage system, the FGD purge water optionallyundergoes some pre-processing before entering the wastewaterconcentrator 14. For example, the conduit 16 optionally operativelyconnects the absorber 46 and a piece of pre-processing equipment 50 todeliver the FGD purge water to the pre-processing equipment 50 forming afirst stage. The conduit 16 operatively connects the pre-processingequipment 50 and the inlet 17 to deliver the feed wastewater to thewastewater concentrator 14 after processing in the pre-processingequipment 50, thereby forming a second stage. The pre-processingequipment 50 may be any type of pre-processing system that is notincompatible with the eventual processing of the feed wastewater in thewastewater concentrator 14. In other arrangements, the feed wastewateris not pretreated, in which case the pre-processing equipment 50 isomitted and the conduit 16 connects directly to the wastewaterconcentrator 14.

In some optional arrangements, cooling tower purge water additionally oralternatively is drawn from cooling water from a cooling tower 52 andsupplied in the feed wastewater to the wastewater concentrator 14. Forexample, a conduit 54 operatively connects the cooling tower 52 to theinlet 17 by operatively connecting with the conduit 16 or directly tothe inlet 17. The conduit 54 optionally is operatively connected to thepre-processing equipment 50 to conduct the cooling tower purge water toand through the pre-processing equipment 50 before the cooling towerpurge water is supplied to the wastewater concentrator 14 as part of thefeed wastewater.

In some optional arrangements, service water from other variousprocesses and equipment additionally or alternatively is supplied in thefeed wastewater to the wastewater concentrator 14. For example, aconduit 56 operatively connects service water, which is collected atvarious locations and/or other equipment within the plant showngenerally at 57, to the wastewater concentrator 14. The conduit 56optionally is operatively connected to the conduit 16, thepre-processing equipment 50 to pre-process the service water beforeentering the wastewater concentrator 14, and/or directly to the feedwastewater entering the inlet 17. Thus, service water from throughoutthe plant may be additionally or alternatively supplied to thewastewater concentrator 14 in a similar manner. In another example, thethermoelectric power plant 12 may generate power plant leachate, such asleachate or runoff from a waste disposal area, such as a landfill area,where solid or semi-solid waste products, such as gypsum, fly ash,and/or other waste products, are held. In such case, the wastewaterconcentrator 14 in some arrangements can be operatively connected with asource of the power plant leachate such that the power plant leachate issupplied to the wastewater concentrator 14 for processing. In a furtherexample, the thermoelectric power plant may include one or more holdingreservoirs for mixed water and waste materials, such as a holding pond,evaporation pond, settling pond, or open-topped settling tank, whichholds water that may include various waste materials. In such case, thewastewater concentrator 14 may be operatively connected with the holdingreservoir such that water from the holding reservoir is supplied to thewastewater concentrator 14 for processing. The sources of power plantleachate and the holding reservoir may also be schematically identifiedat 57. Thus, it is understood that the feed wastewater supplied to thewastewater concentrator 14 may include any one or more of the exemplarysources of wastewater described herein and/or may include other types ofwastewater that may be produced or found at a power plant.

The hot feed gases in some optional arrangements are heated with wasteheat from other processes in the power plant 12 and/or by a dedicatedheating system. In the exemplary arrangement shown in FIG. 1, the hotfeed gases are heated either directly or indirectly with a slip streamof flue gases diverted from the main stream 32 of flue gases, such asalong the conduit 18. The slip stream may be pulled from one or moredifferent locations along the main stream 32. In the exemplaryarrangement, the conduit 18 is operatively connected to the main stream32 to draw off hot flue gases between the economizer 34 and the airpre-heater 36. However, the conduit 18 may also or alternatively beoperatively connected to the main stream 32 to draw off hot flue gasesbetween the boiler 30 and the economizer 34, between the air pre-heater36 and the fly ash removal device 42, between the fly ash removal device42 and the wet scrubber 44, and/or between the wet scrubber 44 and theabsorber 46. The hot feed gases may have a temperature of betweenapproximately 150° F. and approximately 800° F. depending on where theslip stream is connected to the main stream 32 and whether the heatingarrangement for the hot gas is direct or indirect. The hot flue gasesmay be provided directly into the wastewater concentrator 14 and/or maybe used to indirectly heat clean or cleaner gases/air, such as through aheat exchanger. Other sources of waste heat inside the power plant 12,such as from flares, burners, steam condensers, and engines, may also oralternatively be used to heat the hot feed gases supplied to thewastewater concentrator 14 at the inlet 19. In one arrangement, the hotfeed gases are drawn from heated air produced by the combustion airpre-heater 36, as shown at optional conduit 18″ operatively connectingthe combustion air pre-heater 36 with the wastewater concentrator 14.The heated air from the combustion air pre-heater 36 optionally may befurther heated before being provided as hot feed gases, for example,with a flare or a burner 18 a operatively disposed along the conduit18″. The conduit 18″ may connect directly to the inlet 19 or may beoperatively connected to the inlet 19 through, for example, a connectionwith the conduit 18. In addition or alternatively, the hot feed gasesmay be direct fired by a flare or burner, which may be dedicated forheating the feed gases, prior to being supplied to the inlet 19. Inanother arrangement, the wastewater concentrator 14 is operativelyconnected to a piece of standby electrical generation equipment, such asa standby gas turbine or other peak shaving electrical generation device(not shown), such that hot waste gases or heated air generated by theequipment is supplied to the wastewater concentrator 14 for heating thefeed wastewater in a similar manner as described herein. It is alsocontemplated that, in some arrangements, the wastewater generator 14 isoperatively connected to a plurality of different waste heat sources,such as any one or more of the waste heat sources described herein orother waste heat sources, so as to provide hot feed gases to the inlet19 for heating the feed wastewater. An advantage of using waste heatfrom other processes in the power plant 12, such as the hot flue gasfrom the boiler 30, may be gaining more efficiencies and/or reducingnegative environmental impact by reducing the loss of unused waste heatto the atmosphere.

As seen diagrammatically in FIG. 2, the wastewater concentrator 14incorporates a direct contact adiabatic concentration system. Thewastewater concentrator 14 includes the wastewater feed inlet 17, thehot feed gas inlet 19, a direct contact evaporative section 58, agas-liquid separator 60, the gas discharge outlet 22, and the brinedischarge outlet 24. The wastewater feed inlet 17 and the hot feed gasinlet 19 open into the direct contact evaporative section 58. In thedirect contact evaporative section 58, hot feed gas and feed wastewaterare directly contacted with each other, such as by direct intermixing,to form a high-surface area gas-water interface from which water fromthe feed wastewater evaporates into the feed gases without requiring theaddition of dedicated heat energy, such as from a burner, to achieverapid evaporation of the water into the feed gases. Rather, rapidevaporation is achieved by forming the high surface area gas-waterinterface by, for example, rapid mixing of a continuous air volume witha discontinuous water volume, such as through a venturi device as shownand described in any of U.S. Patent Application Publication No.2013/0037223, U.S. Patent Application Publication No. 2010/0236724, andU.S. Patent Application No. 61/673,967, filed Jul. 20, 2012, or by rapidmixing of a continuous water volume with a discontinuous air volume,such as in a submerged gas evaporator with a draft tube as described inU.S. Pat. No. 7,416,172. In one preferred arrangement, the wastewaterconcentrator 14 includes one or more aspects of the LM-HT® wastewaterevaporator, offered by Heartland Technology Partners, LLC, of 9870 BigBend Blvd, St. Louis, Mo. The wastewater concentrator 14 may include anyone or more aspects and features disclosed in the above-indicatedpatents and patent applications, each of which is incorporated byreference herein in its entirety. The direct contact evaporative section58 is operatively connected to the gas-liquid separator 60, for examplewith a conduit and/or opening, to allow the mixed gases, which includesthe feed gas and water vapor evaporated from the wastewater, and thewastewater entrained therein to travel into the gas-liquid separator 60.The wastewater entrained in the mixed gases exiting the direct contactevaporative section 58 is separated from the mixed gases in thegas-liquid separator 60. The gas-liquid separator 60 may be a cross-flowgas-liquid separator, wherein a stream of the mixed gases and entrainedliquids is forced through one or more demister panels to separate theentrained liquids from the gases. Alternatively, the gas-water separator60 may be a cyclonic gas-liquid separator, or a combination ofcross-flow and cyclonic gas-liquid separators. Within cyclonicgas-liquid separators, a stream of gases and entrained liquids is forcedthrough a cyclone chamber to separate entrained liquids from the gases.In one arrangement, the wastewater concentrator 14 is sized to have aprocessing through rate of approximately 30 gallons per minute (gpm) offeed wastewater, including new wastewater and recycled wastewater fromthe discharge brine, and/or produces a discharge brine having betweenapproximately 30% and 60% TDS. In other arrangements, the wastewaterconcentrator 14 may be sized to have a higher processing through rate,for example of 60 gpm, 100 gpm, 200 gpm, or more, a lower processingthrough rate, for example of 30 gpm or less, and any processing throughrate within these ranges. The wastewater concentrator 14 is preferablypermanently installed in the thermoelectric power plant 12.Alternatively, the wastewater concentrator 14 is portable and may betemporarily installed in the thermoelectric power plant 12.

FIG. 4 shows one exemplary arrangement of the wastewater concentrator 14that incorporates a direct contact adiabatic concentration system,wherein the direct contact evaporative section 58 includes a venturidevice 62 and the gas-liquid separator 60 includes a cross flowgas-liquid separator 64. The conduit 18 is connected to the inlet 19,which opens into the venturi device 62 to supply hot feed gases into thewastewater concentrator 14. The conduit 16 is connected to the inlet 17,which opens into the venturi device 62 to supply feed wastewater intothe wastewater concentrator 14. The hot feed gases and the feedwastewater are forced through a narrowed throat of a venturi, whichincreases velocity compared to the velocity of gases through the conduit18, where the hot feed gases and the feed wastewater are thoroughlymixed together to cause rapid evaporation of water vapor. From thethroat of the venturi device 62, the mixed wastewater and gases aredirected through a conduit 66 into the cross flow gas-liquid separator64. The cross flow gas-liquid 64 separator includes an outer shell 68forming an interior space, an inlet port 70 into the interior space, andan outlet port 72 out of the interior space, and a plurality of demisterpanels 74 disposed in the interior space between the inlet port 70 andthe outlet port 72. The demister panels 74 are vertically suspended at90° to, and across the gas flow path between the inlet port 70 and theoutlet port 72 arranged to collect entrained wastewater carried by thegases flowing through the interior space and deposit the collectedwastewater in a sump 76 at the bottom of the interior space. The conduit20 is connected to the outlet port 72, and a fan 78 is optionallyoperatively connected to the conduit 20 to impart a negative pressureacross the interior space to draw the gases through the wastewaterconcentrator 14. Additional details regarding this exemplary wastewaterconcentrator 14 are found in the U.S. Patent Application Publication No.2010/0236724 mentioned previously herein.

With reference again to FIGS. 1 and 2, in an exemplary method,wastewater produced by various processes in the thermoelectric powerplant 12, such as purge water from the FGD system 38 and/or the coolingtower 52 and/or service water, is processed within the wastewaterconcentrator 14 according to the following preferred exemplary processsteps. A stream of hot feed gases is provided to the wastewaterconcentrator 14 with the conduit 18 operatively connected to the inlet19. Preferably, the conduit 18 is operatively connected to the main fluegas stream 32 so that the hot feed gases are heated with waste heat fromthe boiler 30. A stream of feed wastewater, including one or more of thepurge waters and/or service water, is provided to the wastewaterconcentrator 14 through one or more conduits 16 operatively connected toone or more inlets 17. The conduit 16 is operatively connected to one ormore sources of the purge waters and/or service water. The hot feedgases are mixed directly with the feed wastewater inside the wastewaterconcentrator 14, such as in the direct contact evaporative section 58,to evaporate water vapor from the feed wastewater. Preferably, the hotfeed gases and the feed wastewater are mixed by being directed through aventuri device. The water vapor and gases are then separated fromentrained concentrated wastewater in the wastewater concentrator 14,such as inside the gas-liquid separator 60, thereby forming aconcentrated discharge brine and discharge gases. The discharge brineincludes the concentrated wastewater separated from the water vapor andthe gases. The discharge gases include the gases and the water vapor.Thereafter, the discharge gases are exhausted from the wastewaterconcentrator 14, such as through the exhaust outlet 22 and through theconduit 20. The discharge brine is discharged, either periodically orcontinuously, from the wastewater concentrator 14 through the dischargeoutlet 24.

In one option, the discharge brine is supplied to the post-processingequipment 26, including a solid-liquid separator. The solid-liquidseparator separates solids and liquids in the brine. The liquids arereturned, for example with a return conduit 80 operatively connectingthe solid-liquid separator to one of the inlets 17, for reprocessingthrough the wastewater concentrator 14. The solids are removed from thesolid-liquid separator for further processing, repurposing, and/ordisposal.

Turning to FIG. 3, in addition to the process steps describedpreviously, additional and alternative optional exemplary processingsteps are shown for processing the wastewater from the thermoelectricpower plant 12 with the wastewater concentrator 14. In this exemplaryarrangement, the conduit 16 is operatively connected to the FGD system38 to supply FGD purge water as part of the feed wastewater supplied tothe inlet 17 of the wastewater concentrator 14. The FGD purge water ispre-treated, such as by the pre-processing equipment 50 operativelydisposed along the conduit 16, prior to entering the wastewaterconcentrator 14. The conduit 18 is operatively connected to the mainflue gas stream 32. A fly ash removal device 82, such as an ESP, WESP,or filter bag, is preferably operatively disposed along the conduit 18to remove and/or reduce fly ash and/or other particulates from the fluegas prior to entering the wastewater concentrator 14. Alternatively oradditionally, hot flue gases from the main flue may be provided to thewastewater concentrator 14 without being treated, such as by a conduit18′ having a first end operatively connected to the main flue gas stream32 and a second end operatively connected to the inlet 19 of thewastewater concentrator 14. In some arrangements, a controlled amount offly ash may be provided into the feed wastewater, either byreintroduction into or incomplete removal from, the stream of feedwastewater. The conduit 20 is operatively connected with additionalemission control equipment, such as a reheater 84. The discharge gasesare conducted to the reheater 84 via the conduit 20. The reheater 84heats or re-heats the discharge gases from the wastewater concentrator14, such as with a flare, burner, or another stream of heated gases,preferably to a temperature above an acid-gas condensation temperatureappropriate for the makeup of the discharge gases. Thereafter, there-heated discharge gases are returned to the plant exhaust system, suchas to the exhaust stack 40, and/or are returned for re-use in otherequipment within the plant, such as the FGD system 38. Further, solidsremoved from the solid-liquid separator 26 are directed, such as by aconduit 86, to additional post-processing equipment 26′ for furthertreatment. The solids are removed from the post-processing equipment 26′and transported away for disposal, such as sale, repurposing,landfilling, etc.

Turning to FIG. 5, in some preferred arrangements, the pre-processingequipment 50 shown in FIGS. 1 and 3 includes one or more containedair-water interface liquid evaporators, such as liquid evaporators 90,90′, and/or 90″, operatively disposed in a reservoir 92 of wastewaterobtained from one or more of the processes within the power plant 12.The reservoir 92 may be a tank or a pond open to the environment, forexample. At least one or more sources of wastewater from the power plant12, such as the conduits 16, 54, and/or 56, are operatively connected toone or more inlets 94 a into the reservoir 92 to provide wastewater fromthe power plant 12 into the reservoir 92. Another portion of the conduit16 operatively connects one or more outlets 94 b of the reservoir 92 tothe inlet 17 of the wastewater concentrator 14 to transfer thewastewater from the reservoir 92 to the wastewater concentrator 14. Thewastewater may include FGD purge water, cooling tower purge water,service water, power plant leachate, and/or holding reservoir water, asdescribed previously herein. The liquid evaporator 90 is alsooperatively connected to a source of forced air, such as a fan 93. Theforced air optionally is heated by one or more sources of waste heat inthe power plant in a manner as described elsewhere herein. Preferably,the fan 93 is operatively connected by a conduit 95 to blow the air intothe liquid evaporator. The fan 93 may be, for example, any type ofblower sufficient and arranged to force the hot gases the air into theliquid evaporator 90 so as to achieve vigorous air-water mixing asdescribed in more detail below. The liquid evaporator 90 pre-treats thepower plant wastewater by evaporating some water out of the wastewater,thereby providing a more concentrated stream of the wastewater to besupplied into the wastewater concentrator 14. Thus, using the liquidevaporator 90 as part of a pre-treatment step at the pre-processingequipment 50 can improve the output of the wastewater concentrator 14 byreducing the treatment time to obtain the desired degree ofconcentration for brine discharged from the wastewater concentrator 14.Further, heating the air forced into the liquid evaporator 90, forexample, with waste heat from the power plant, improves theeffectiveness of the liquid evaporator 90. If the air is heated fromwaste heat produced in the power plant 12, the liquid evaporator 90 mayfurther improve the energy efficiency of the power plant 12. Inaddition, other exemplary contained air-water interface liquidevaporators, such as the liquid evaporators 90′ and/or 90″ as shown inFIGS. 6 and 7, may additionally or alternatively be operatively disposedin the reservoir 92 to pre-treat the wastewater at the pre-processingequipment 50. Although described in relation to use in the environmentof the power plant 12, any one of the liquid evaporator 90, 90′, 90″ maybe used to pre-process wastewater prior to being provided for processingin the wastewater concentrator 14 as part of a wastewater treatmentsystem in other industrial settings, either alone or in combination withother devices. Thus, the combination of a liquid evaporator 90, 90′, or90″ as a pre-processing device for wastewater being processed by thewastewater concentrator 14 is not limited to use in the power plant 12.A brief description of each of the exemplary liquid evaporators 90, 90′,and 90″ is provided herein. Additional detailed description of theliquid evaporators 90, 90′, and 90″ may be found in U.S. PatentApplication No. 61/614,601, which is incorporated by reference herein inits entirety.

In the exemplary arrangement of FIG. 5, the liquid evaporator 90 has abody defining a partially enclosed vessel 96 that floats or is otherwisemaintained in a position in the reservoir 92 of wastewater such that thetop surface of the wastewater is located between a top portion of thevessel disposed above the wastewater and a bottom portion of the vesseldisposed in the wastewater. The vessel 96 defines an interior space 98that is confined by the walls of the vessel. An opening 100 through asubmerged portion of the vessel 96 allows wastewater to enter into thebottom portion of the interior space 98 confined within the vessel 96.The bottom portion of the interior space 98 is in fluid communicationwith the upper portion of the interior space 98 such that water vapormay travel from the bottom portion into the top portion. The top portionof the interior space 98 at least partly defines an exhaust path A fromthe top surface of the wastewater inside the vessel 96 to one or moreexhaust ports 102 to the surrounding environment. The exhaust ports 102are operatively located above the top surface of the wastewater. An airdowncomer 104 is arranged to be connected to an air supply line, such asthe conduit 95. The air downcomer 104 has a discharge outlet 106disposed inside the bottom portion of the interior space 98. Thedischarge outlet 106 may include an open bottom end 106 a of the airdowncomer 104. The discharge outlet 106 includes a plurality of spargeports 106 b through the sidewall of the air downcomer 104 adjacent theopen bottom end 106 a. The area where the discharge outlet 106 islocated inside the bottom portion of the confined space 98 forms an airentrainment chamber 108 during operation of the liquid evaporator. Inoperation, an air pump, such as the fan 93, forces air through the airdowncomer 104 into the air entrainment chamber 108, where the airdisplaces wastewater causing wastewater to flow upwards into the bottomopen end 100 of the air entrainment chamber 108 and through the interiorspace 98, thereby establishing vigorous mixing of the air with thewastewater. The air-water mixture then moves naturally to the topsurface of the wastewater inside the confined interior space 98, wherethe air and water vapor separates from the wastewater, for example, bybubbling. From the top surface of the wastewater inside the interiorspace 98, the air and water vapor travels through the exhaust pathway Ato be exhausted out of the vessel 96 through the exhaust ports 102 asmoist exhaust air containing water vapor, while concentrated wastewaterand contaminants are trapped within the vessel 96 and returned to thewastewater. In this manner, water is evaporated and separated out fromthe contaminants without allowing uncontrolled dispersion of thewastewater mist or spray into the surrounding environment. The liquidevaporator 90 may be maintained in the operative position at the topsurface of the wastewater in the reservoir 92 by any convenientmechanism, such as support legs, a suspension structure, and/orflotation.

In one optional arrangement, the interior space 98 of the vessel 96includes an upper chamber 110, a middle chamber 112, and a lower chamber114, which are in fluid communication with each other. An open bottomend of the lower chamber 114 defines the opening 100. An open top end ofthe lower chamber 114 connects with an opening at the bottom of themiddle chamber 112. In the operative position, the top level of thewastewater extends through the middle chamber 112, such that the lowerchamber 114 and a lower portion of the middle chamber 112 are disposedin the wastewater, and the upper chamber 110 and the upper portion ofthe middle chamber 112 are disposed above the wastewater. The airentrainment chamber 108 is defined inside the lower chamber 114.Flotation devices 116 carried by the vessel 96 are located so as tomaintain the liquid evaporator 90 in the operative position. The exhaustports 102 are directed downwardly toward the top surface of thewastewater. The downcomer 104 extends down through the top of the vessel96, into and through the upper chamber 110 and the middle chamber 112,and into the lower chamber 114. The discharge outlet 106 is spaced abovethe opening 100 a space sufficient to ensure that air discharged throughthe discharge outlet 106 does not exit through the opening 100 undernormal operating conditions. A baffle 118 separates the upper chamber110 from the middle chamber 112. Openings 120 through the baffle 118allow water vapor to pass from the middle chamber 112 to the upperchamber 110. Demisting structures 122 are disposed in the upper chamberin and/or across the exhaust path A to form a tortuous path from theopenings 120 to the exhaust ports 102. Liquid discharge tubes 124 a, 124b extend down from the middle chamber 112 on opposite sides of the lowerchamber 114. The liquid discharge tubes 124 a, 124 b merge into a singledischarge riser 124 c below the vessel 96. An air vent tube 124 d islocated at the top of the discharge riser 124 c at the junction of thedischarge pipes 124 a and 124 b. The air vent tube 124 d issubstantially smaller than the liquid discharge tubes 124 a, 124 b ordischarge riser 124 c. The discharge riser 124 c extends downwardlytoward the bottom of the reservoir 92. As air is pumped through thedowncomer 104 into the lower chamber 114, the water circulates upwardlyin the air entrainment chamber 108 to the middle chamber 112, movesradially outwardly in the middle chamber 112, and then travels from themiddle downwardly into the liquid discharge tubes 124 a, 124 b. Thewater is discharged back into the reservoir 92 out of one or moreopenings in the discharge riser 124 c. The liquid evaporator 90 ispreferably fabricated almost entirely from plastics, such as polyvinylchloride, polypropylene, or high density polyethylene.

In the exemplary arrangement of FIG. 6, the liquid evaporator 90′ isadapted for use in a multi-stage system that uses the evaporator 90′ asan intermediate in-line unit with a connection for transferring theexhaust water vapor to another processing step, such as another liquidevaporator 90, 90′, or 90″, or to a remote exhaust location. The liquidevaporator 90′ is substantially similar to the liquid evaporator 90 withthe exception that, in the upper chamber 110, the liquid evaporator 90′has only a single exhaust port 102 for connection to another transferconduit instead of a plurality of exhaust ports 102, and the liquidevaporator 90′ has a single bustle 130 instead of the baffles 122. Thevessel 96, the downcomer 104, and the exhaust path A are preferablyarranged radially symmetrically about a vertical axis Z, and the exhaustport 102 is non-symmetrically arranged about the vertical axis Z at asingle location on one side of the top chamber 110. All other portionsof the evaporator 90′ are preferably the same as the correspondingportions on the evaporator 90 and will not be described again for thesake of brevity. The bustle 130 is arranged to allow thenon-symmetrically located exhaust port 102 to draw off air and watervapor from inside the top chamber 110 so as to maintain radiallysymmetrical flow of air upwardly from the sparge ports 106 b and throughthe lower and middle chambers 114 and 112, by for example, causinguniform radial mass flow of air at all circumferential locations aroundthe bustle 130 from a region inside the bustle 130 radially outwardly toa region outside of the bustle 130 to the exhaust port 102. The bustle130 is formed of a circumferential wall 132, preferably a cylindricalwall, extending upwardly from the baffle 118 part way to the topinterior wall of the upper chamber 110. The circumferential wall 132 isspaced radially between the outer peripheral wall of the upper chamber110 and the openings 120, thereby forming an inner volume encompassed bythe bustle 130 and an outer peripheral volume between the bustle 130 andthe outer peripheral wall. The circumferential wall 132 defines a gap134 between the inner volume and the outer peripheral volume. The gap134 has a width W between a top edge of the circumferential wall 132 anda top wall of the upper chamber 110. The width W of the gap 134 iscontinuously variable along the length of the wall 132. The gap 134 hasa smallest width W (e.g., the wall 132 is tallest) immediately adjacentthe location of the exhaust port 102. The gap 134 has a largest width Wdiametrically opposite the location of the exhaust port 102. In thepresent example, the circumferential wall 132 is cylindrical and the topedge defines an inclined plane with its highest point adjacent theexhaust port 102 and its lowest point diametrically opposite from theexhaust port 102. Preferably, the width W of the gap 134 is arranged tovary so the velocity of exhaust air is constant through any verticalcross-section of the gap 134 that is in a plane perpendicular to conduit106 Other bustle designs capable of providing or improving uniformradial mass flow of the air outwardly from the inner volume are alsopossible, such as those disclosed in U.S. Pat. No. 7,442,035, which isincorporated by reference herein in its entirety. The exhaust port 102is optionally connected to a conduit 136 that is operatively connectedto another instrument, such as another evaporator 90, 90′, or 90″. Theexhaust port 102 may alternatively exhaust to air or be connected tosome other device.

In the exemplary arrangement of FIG. 7, the liquid evaporator 90″ issubstantially similar to the liquid evaporators 90 and/or 90′, but withthe addition of an adjustable stabilization system 140 and twoadditional discharge tubes 124 e and 124 f. Like the previouslydescribed liquid evaporators 90 and 90′, the liquid evaporator 90″ alsoincludes the partially enclosed vessel 96 having the middle chamber 112disposed between the upper chamber 110 and the lower chamber 114, theair supply downcomer 104 arranged for connection to an air supply line,such as the conduit 95, for injecting air into the air entrainmentchamber 108 formed by the lower chamber 114, and internal baffles 122and/or the bustle 130 (not visible) arranged in the upper chamber 110 toprovide a tortuous path to one or more exhaust outlets 102. Thedischarge tubes 124 a,b,e, f are preferably radially spaced equally fromthe axis Z and preferably spaced at 90° on center around the outerperiphery. Further, the outer annular periphery of the lower chamber 114is spaced radially inwardly from the discharge tubes 124 a,b,e,f ratherthan being located immediately adjacent the discharge tubes as shown forthe liquid evaporators 90 and 90′. Preferably, remaining features of thepartially enclosed vessel 96 are identical to corresponding features ineither of the liquid evaporators 90 or 90′ and can be understood withreference to the prior descriptions thereof. The adjustablestabilization system 140 is arranged to help stabilize the liquidevaporator 90″ in an upright operative position, i.e., with the axis Zaligned generally vertically, the lower chamber 114 disposed in thewastewater, and the upper chamber 110 disposed above the wastewaterwhile air is being forced through the air supply downcomer 104 into thelower chamber 114. The stabilization system 140 includes flotationdevices 142 operatively secured to the vessel 96 by outriggers 144. Theposition of the flotation devices 142 may be adjusted axially and/orradially to cause the vessel 96 to sit higher or lower in thewastewater. The flotation devices 142 are disposed diametricallyopposite each other on opposite sides of the vessel 96. Each flotationdevice 142 preferably is spaced radially from the outer annularperiphery of the vessel and sized to provide sufficient buoyancy to holdthe upper chamber 110 spaced above the top surface of the wastewater.The outriggers 144 are formed by two struts arranged in parallel onopposite sides of the downcomer 104 and connected to the top of thevessel. Each strut extends outwardly from opposite sides of the outerannular periphery of the upper chamber 110, and each flotation device142 is attached near the ends of the struts. One or more hinges 146 inthe struts are spaced from the outer annular periphery of the upperchamber 110 and arranged to allow the flotation devices 142 to beselectively raised and/or lowered by pivoting the ends of the strutsaround the respective hinges. The flotation devices 142 are preferablydisposed spaced along an axis of the conduit 95 over the top of thevessel 96 approaching the downcomer 104. The flotation devices 142 arearranged to counteract rotational forces that act to tip the vessel 96away from substantially vertical alignment in response to air beingforced through the conduit 95.

The systems, apparatuses, and methods for treating flue gasdesulfurization purge water and other forms of wastewater disclosedherein may be useful to address water-use for thermoelectric generatingunits, particularly such units that rely on burning hydrocarbon fuels,such as coal. In some applications, the systems, apparatuses, andmethods may be implemented as important components of or for zero-liquiddischarge (ZLD) treatment systems, moisture recovery, wastewatertreatment, landfill management, water management for carbon dioxidetechnologies, cooling tower and advanced cooling system technologies,and/or integrated water management and modeling in thermoelectricgenerating units. The systems, apparatuses, and methods may help anoperator of a thermoelectric generating unit to increase water usageand/or re-usage efficiency, reduce water withdrawal and/or consumption,and/or meet water discharge limits. The technologies disclosed herein insome arrangements may provide a cost effective treatment alternative tocurrently known treatment processes for flue gas desulfurization purgewater and other types of wastewater. The technologies disclosed hereinmay reduce power consumption and/or capture wastewater pollutants with amore efficient process for environmentally friendly disposal ofdischarge pollutants.

Additional modifications to the systems, apparatuses, and methodsdisclosed herein will be apparent to those skilled in the art in view ofthe foregoing description. Accordingly, this description is to beconstrued as illustrative only and is presented for the purpose ofenabling those skilled in the art to make and use the invention and toteach the best mode of carrying out same. The exclusive rights to allmodifications which come within the scope of the appended claims arereserved.

We claim:
 1. A multi-stage wastewater treatment system comprising: areservoir adapted to contain wastewater therein; a contained air-waterinterface liquid evaporator arranged to be operatively disposed in thereservoir, the contained air-water interface liquid evaporator includinga partially enclosed vessel arranged to be operatively disposed in thewastewater and defining a confined space including an air entrainmentchamber, an air downcomer to blow air into the wastewater inside themixing chamber, and a first exhaust port arranged to be operativelydisposed above the wastewater and to allow water vapor to escape fromthe mixing chamber; and a wastewater concentrator separate from thecontained air-water interface liquid evaporator, the wastewaterconcentrator comprising a direct contact adiabatic wastewaterconcentrator system, the wastewater concentrator operatively connectedto the reservoir to receive a stream of wastewater from the reservoirand to form additional water vapor and concentrated wastewater from thestream of wastewater, wherein the wastewater concentrator comprises asump to collect the concentrated wastewater and a second exhaust portarranged to allow the additional water vapor to escape from thewastewater concentrator.
 2. The multi-stage wastewater treatment systemof claim 1, wherein the wastewater concentrator comprises a directcontact evaporator section and a gas-liquid separator section.
 3. Themulti-stage wastewater treatment system of claim 2, wherein the directcontact evaporator section comprises a venturi device arranged to mixhot feed gases directly with the stream of wastewater and to evaporatewater from the stream of wastewater to form the additional water vaporand the concentrated wastewater.
 4. The multi-stage wastewater treatmentsystem of claim 3, wherein the direct contact evaporator section isoperatively connected to a source of waste heat from a thermoelectricpower plant to provide the hot feed gases.
 5. The multi-stage wastewatertreatment system of claim 3, wherein the gas-liquid separator sectioncomprises a cross flow gas-liquid separator comprising an outer shelldefining the second exhaust port and an interior space and at least onedemister disposed in the interior space, the cross flow gas-liquidseparator arranged to separate the additional water vapor from theconcentrated wastewater and to exhaust discharge gases from thegas-liquid separator section, including the additional water vapor andsome or all of the feed gases, through the second exhaust port.
 6. Themulti-stage wastewater treatment system of claim 1, wherein thecontained air-water interface liquid evaporator comprises: a fanoperatively arranged to force air through the air downcomer into the airentrainment chamber; and, a tortuous pathway connecting the airentrainment chamber to the exhaust port.
 7. The multi-stage wastewatertreatment system of claim 6, wherein the vessel is arranged to bedisposed in an operative position at a top surface of the wastewaterhaving a top portion to be disposed above the top surface and a bottomportion to be disposed in the wastewater.
 8. The multi-stage wastewatertreatment system of claim 7, wherein the contained air-water interfaceliquid evaporator includes a flotation device operatively secured to thevessel, wherein the flotation device is arranged to maintain the vesselin the operative position by floating on the top surface of thewastewater.
 9. The multi-stage wastewater treatment system of claim 7,wherein the liquid evaporator section is maintained in a fixed positionin the operative position by braces or legs.
 10. The multi-stagewastewater treatment system of claim 1, further comprising at least asecond contained air-water interface liquid evaporator operativelydisposed in the wastewater.
 11. The multi-stage wastewater treatmentsystem of claim 1, wherein the reservoir is an open reservoir.
 12. Themulti-stage wastewater treatment system of claim 1, wherein the airdowncomer is operatively connected to a source of heat to heat the airblown into the wastewater.
 13. The multi-stage wastewater treatmentsystem of claim 11, wherein the air downcomer is operatively connectedto a source of waste heat in a thermoelectric power plant.
 14. A methodof treating wastewater comprising the steps of: providing wastewaterhaving a first concentration into a reservoir; evaporating water vaporfrom the wastewater in the reservoir with a contained air-waterinterface liquid evaporator at a first stage to produce concentratedwastewater; exhausting the water vapor from inside the containedair-water interface liquid evaporator at a first exhaust port;transferring the concentrated wastewater to a wastewater concentratorcomprising a direct contact adiabatic wastewater concentrator system;and evaporating additional water vapor from the concentrated wastewaterwith the wastewater concentrator at a second stage to produce aconcentrated discharge brine and additional water vapor; separating theadditional water vapor from the concentrated discharge brine in thewastewater concentrator; collecting the concentrated discharge brine ina sump; and exhausting the additional water vapor from inside thewastewater concentrator at a second exhaust port.
 15. The method oftreating wastewater of claim 14, wherein the contained air-waterinterface liquid evaporator comprises a partially enclosed vesseldisposed in the wastewater, an air entrainment chamber disposed insidethe vessel, and the first exhaust port from the vessel in fluidcommunication with the air entrainment chamber, the method furthercomprising the steps of: disposing the vessel at a top surface of thewastewater; forcing air into the wastewater inside the air entrainmentchamber; vigorously mixing the air and the wastewater inside the airentrainment chamber; and exhausting the water vapor from the airentrainment chamber out through the first exhaust port.
 16. The methodof treating wastewater of claim 14, wherein the wastewater concentratorcomprises a direct contact evaporator section including a venturidevice, and wherein the step of evaporating additional water comprisesmixing a stream of hot feed gases directly with a stream of theconcentrated wastewater and evaporating the additional water vapor fromthe wastewater in the venturi device.
 17. The method of treatingwastewater of claim 16, further comprising the step of obtaining thestream of hot feed gases at least partially from a source of waste heatin an industrial plant.
 18. The method of treating wastewater of claim17, wherein the industrial plant comprises a thermoelectric power plant,and wherein the step of obtaining comprises the step of obtaining hotfeed gases from a stream of hot flue gases from a boiler.
 19. The methodof treating wastewater of claim 16, wherein the wastewater concentratorcomprises a gas-liquid separator section, and wherein the step ofseparating comprises separating the additional water vapor from theconcentrated wastewater in the gas-liquid separator section andexhausting discharge gases from the gas-liquid separator section,including some or all of the additional water vapor and the feed gases,at the second exhaust port.